The external electron donor in Ziegler-Natta polymerization act as stereoselective control agents (SCA) to control the amount of atactic or non-stereo regular polymer produced during the reaction. The external electron donor for olefin polymerization when added to the catalytic system as a part of co-catalyst retains the stereospecificity of the active sites, convert non-stereospecific sites to stereospecific sites, poisons the non-stereospecific sites and also controls the molecular weight distributions while retaining high performance with respect to catalytic activity. Alkoxy silanes are used extensively as external electron donor for olefin polymerizations for Ziegler-Natta catalysts containing phthalates and diethers as internal donors. These donors impart different polymer properties depending upon the number and type of alkoxy group present in the alkoxy silane. Mixed alkoxy silane donors are also reported to be used for preparing polymers having enhanced properties.
The concept of activity limiting agent (ALA) was introduced with the explanation of self extinguishing nature of catalyst composition to avoid fouling of the reactor due to softening of the polymer during elevated polymerization temperature. This specifically is very important in those polymerization conditions where high temperatures are involved specifically in gas phase. U.S. Pat. No. 7,989,383 cites that catalyst composition having ethyl benzoate as internal donor when are used for polymerization along with p-ethoxy ethylbenzoate (PEEB) have inherent property of self extinguishing. This patent describes a catalyst composition having procatalyst, cocatalyst, selectivity control agent (SCA) comprising one or more silicon containing compounds and an activity limiting agent (ALA) selected from the group consisting of distearyl 3,3-thiodipropionate, butanedioic acid polymer with 4-hydroxy-2,2,6,6-tetramethyl-1-piperidineethanol, bis(2,2,6,6,-tetramethyl-4-piperidyl)sebacate, pentaerythritol tetrakis[3-(3′,5′-di-t-butyl-4′-hydroxyphenyl)propionate], and combinations thereof.
U.S. Pat. No. 7,381,779 describes mixture of two or more different selectivity control agents comprising aromatic monocarboxylic acids or substituted derivatives and alkoxysilane compounds.
U.S. Pat. No. 7,781,363 describes a selectivity control agent having at least one silicon containing compound containing at least one C1-10 alkoxy group bonded to a silicon atom, and activity limiting agent (ALA) compounds comprising one or more aliphatic or cycloaliphatic carboxylic acids; alkyl-, cycloalkyl- or alkyl(poly)(oxyalkyl)-(poly)ester derivatives thereof or inertly substituted derivatives.
U.S. Pat. No. 7,893,003 provides a Ziegler-Natta catalyst composition comprising a procatalyst, a cocatalyst and a mixed external electron donor comprising a first selectivity control agent, a second selectivity control agent, and an activity limiting agent. This catalyst composition produces a high-stiffness propylene-based polymer with a melt flow rate greater than about 50 g/10 min. The polymerization process occurs in a single reactor, utilizing standard hydrogen concentration with no visbreaking. SCA1 comprises dicyclopentyldimethoxysilane, SCA2 is selected from the group consisting of methylcyclohexyldiethoxysilane, di-isobutyldiethoxysilane, n-propyltriethoxysilane, tetraethoxysilane, di-n-butyl-dimethoxysilane, benzyltriethoxysilane, but-3-enyltriethoxysilane, 1-(triethoxysilyl)-2-pentene, (triethoxysilyl)cyclohexane, and combinations thereof or, 1-ethoxy-2-n-pentoxybenzene and ALA comprises of C1-4 alkyl ester of aliphatic C8-20 monocarboxylic acid and/or isopropyl myristate.
U.S. Pat. No. 7,678,868 describes the usage of a mixture of a selectivity control agent comprising one or more silicon containing compounds and an activity limiting agent selected from the group consisting of a C1-20 alkyl ester of an aliphatic C8-20 monocarboxylic acid, a C2-20 alkyl mono- or poly-carboxylate derivative of a C2-100 polyglycol, and combinations thereof for propylene ethylene copolymerization.
U.S. Pat. No. 7,491,670 describes selectivity control agent comprising of alkoxy silane and activity limiting agent (ALA) compounds comprising one or more aliphatic or cycloaliphatic carboxylic acids; alkyl-, cycloalkyl- or alkyl(poly)(oxyalkyl)-(poly)ester derivatives thereof or inertly substituted derivatives usage in particular molar ratios with respect to transition metal and equivalent ratio of SCA and ALA to be used. Also claimed is the usage in gas phase polymerization and the polymer formed is without an undesired odor.
U.S. Pat. No. 8,993,692 describes the self limiting agent selected from the group of aliphatic, cycloaliphatic, substituted cycloaliphatic or aromatic esters, anhydrides and amides such that the self limiting agent reduces polymerization rates to no greater than 40% of the polymerization rate in the absence of the self limiting agent at temperatures equal to or greater than 120° C. for ethylene polymerization.
The usage of monoethers as external donor is described in: U.S. Pat. No. 6,399,837, U.S. Pat. No. 7,420,022, U.S. Pat. No. 6,271,321, U.S. Pat. No. 4,287,328, U.S. Pat. No. 9,102,770, U.S. Pat. No. 6,534,613, U.S. Pat. No. 6,228,957, U.S. Pat. No. 4,918,037 but none of the prior art describes the ability of monoether as ALA.
The usage of diethers as ALA has been described in: U.S. Pat. No. 8,536,290, U.S. Pat. No. 9,382,342, U.S. Pat. No. 9,382,343, U.S. Pat. No. 9,434,796 with alkoxypropyl ester as an internal electron donor.
It is desirable of those catalyst compositions which act as activity limiting agent as well as selectivity control agent in the polymerization process where the polymerization runs smoothly without any fouling of the reactor while maintaining the total soluble and melt flow properties of the polymer, and enhanced hydrogen response of the catalyst.